JPH0614304B2 - Power supply circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit used in a video disc player, a video tape recorder (VTR) or the like.

2. Description of the Related Art A video disc player, a VTR and the like generally use a commercial power source. Generally, these devices have two or more DC constant voltage power supply circuits with different voltages.
For example, the current consumption of the circuit varies depending on the usage mode of the device such as "standby", "stop", "playback", "recording", and "takeout".

On the other hand, when using a commercial power supply, the two items of voltage fluctuation countermeasures and instantaneous power failure countermeasures among the power source fluctuation factors must always be satisfied, and in the design of the power supply circuit, at the worst input condition, each voltage is the maximum. In the case of load, security was required, which was a problem for power saving and cost reduction.

The conventional example will be described below with reference to FIG.

FIG. 2 shows a DC constant voltage power supply circuit which is widely and commonly used in video disc players and VTRs. The AC power supply E ₁ is supplied from the commercial power supply, and the power transformer 1 supplies 2
Two AC voltages E'2, E'3 are converted into a rectifier circuit 2,
The stabilized voltages of the voltages V3 and V2 are generated by the two DC stabilized power supply circuits 4 and 5 which are rectified by the DC stabilized power supply circuits 3 and 4 and which have different voltages. It is a general voltage that V3 is + 12V and V2 is + 5V. The stabilized voltage V3 on the high voltage side is usually supplied to the audio circuit and the motor control circuit, and the stabilized voltage V2 on the low voltage side is usually supplied to the microcomputer system.

Therefore, the high regulated voltage V3 has a large load fluctuation depending on the mode of the device, and the low voltage V3 often has a small fluctuation.

On the other hand, the fluctuation of the voltage of the commercial power source is ± 10%, with a margin of ± 15%, and that of the momentary power failure is -25%, and about 200 milliseconds must be taken into consideration.

In particular, since the low stabilization voltage V2 in the figure is supplied to the microcomputer, sufficient stabilization is required.

Therefore, in the conventional circuit, the rectified voltage V'that can stabilize V2 and V3 even when E1 is about -25%.
1 and V'4 were secured.

However, in the conventional structure, V'1 and V'4 at the normal voltage are increased due to the voltage design as described above.
Loss power consumption of each constant voltage circuit is large, transistor Q
Since a large amount of heat is generated in 1 and Q2, a large-capacity heat dissipation plate was required. Further, since E'2 and E'3 are increased, the efficiency of the entire power supply circuit is lowered and the cost is increased.

In view of the above problems, it is an object of the present invention to reduce power consumption of a power supply circuit and improve efficiency.

Means for Solving the Problems In order to achieve this object, the present invention inserts a switch circuit, which is turned on when one voltage becomes a certain value or less, between voltage lines of different constant voltage power supply circuits. The above-mentioned two different voltage power supplies are linked-controlled.

Operation With this configuration, the power consumption of the low-voltage side voltage stabilization circuit during normal operation is reduced, and when the commercial power supply voltage drops, the high-voltage side stabilized output voltage is supplied to the low-voltage side line. It is possible to achieve voltage stabilization on the low voltage side, which is highly dependent on the power supply voltage, such as a computer. The switch circuit acts so as to turn on when the voltage on the low voltage side becomes a certain value or less.

Embodiment An embodiment of the present invention will be described below with reference to FIG.

In the figure, 1 is a power transformer, 2 and 3 are rectifier circuits, 4
Is a stabilized power supply circuit on the low voltage side, and 5 is a stabilized power supply circuit on the high voltage side. Further, Q1 and Q2 are voltage control transistors of the respective constant voltage circuits.

Further, Q3, R1, D1 and R2 are transistors, resistors and a constant voltage diode which constitute a switch circuit which is a feature of the present invention. The emitter of the transistor Q3 is connected to the stabilized voltage output terminal on the high voltage side to form a constant voltage diode. The anode of D1 is directly connected to the unregulated voltage terminal on the low voltage side via the resistor R2.

Using the power supply circuit as shown in FIG. 1 in a video disk player, the output V3 of the constant voltage power supply circuit on the high voltage side composed of a rectifying circuit 3, a stabilizing power supply circuit 5, a voltage control transistor Q2, a capacitor C2 and a resistor r2. Is + 12V, the rectifier circuit 2, the stabilizing power supply circuit 4, the voltage control transistor Q1,
The operation of an example in which the output V2 of the constant voltage power supply circuit on the low voltage side including the capacitor C1 and the resistor r1 is set to + 5V will be described.

V2 is supplied to the microcomputer and the logic circuit, and the current changes little depending on the mode of use of the video disk player, and I1 is about 700 mA of the chemical solution.

V3 is supplied to each of the audio, video, and control circuits, and the motor control circuit in particular has a large fluctuation in current consumption. In particular, the turntable motor alone requires about 800 mA when starting and stopping, but about 100 mA during steady rotation. Therefore, the DC I2 including the components of other circuits is
It greatly depends on the mode of use of the video disc player: about 300 mA in normal playback mode, 10 at peak.
It reaches as much as 00mA.

Considering the performance as a power source of the video disc player, V2 must be most stable in the normal reproduction mode, and the start and stop periods of the turntable motor are limited in a short time. At the same time, if a large drop in commercial power such as an instantaneous power failure occurs within this very limited short time, the microcomputer and other logic circuits are reset, and even if the player returns to the initial mode. It does not matter in practice. If I2 in the normal playback mode is set to about 300 mA, there will be a current margin of about 700 mA for the peak load.

Here, the voltage drop of the voltage control transistors Q1 and Q2 is 0.5 V or less of V _CEsat of the transistors, so that the V2 and V3 are stabilized, the unstabilized voltages V1 and V4 are +5.5 V and +12.5 V or more, respectively. Must be secured. However, in the conventional circuit (Fig. 2) that guarantees these V'1 and V'4 up to -25% of E1 as in the case of momentary power failure, the loss power consumption during normal reproduction was large.

Therefore, in FIG. 1, E2 is pressed lower than E′2 in FIG. 2, V1 in FIG. 1 is pressed lower than V′1 in FIG. 2, and E1 is about −1.
Set so that V1 becomes 5.5V at 2%.

On the other hand, E3 and V4 in FIG. 1 are E'3 and V'in FIG.
Set to the same specifications as 4.

The transistor Q3 is a switching power transistor, and is controlled by a voltage comparison circuit including resistors R1, R2 and a constant voltage diode D1. V3 in Figure 1 is +1
It is 2V, and V1 changes according to the change of E1 because I1 is almost constant. When the value of the constant voltage diode D1 is selected and V1 falls below + 5.5V, the transistor Q3 is turned on to reinforce the destabilizing voltage of the low voltage measuring voltage power supply circuit.

By this reinforcement, V2 is completely guaranteed against the reduced voltage of E1 during the normal reproduction, and it is possible to secure the stabilization of V2 at the time of starting and stopping the turntable while sacrificing the stabilization of V3 to some extent.

Further, as described above, the voltage of E2 can be lowered, so that power saving can be achieved.

For example, like the electrostatic capacity type video disc player, the load fluctuation on the high voltage side is large, the load on the low voltage side is constant, and the load on the high voltage side decreases during normal playback. It is extremely effective for a power supply circuit of equipment such as a voltage output of + 12V and a low-voltage side constant voltage output of + 5V, and the winding voltage E2 in FIG. 1 can be reduced by about 13% as compared with FIG.

In addition, as the configuration of the switch circuit, the resistor R2 of FIG.
There is also a method of connecting the constant voltage diode D1 to the collector side of the transistor Q1.

As described above, according to the present invention, not only in the case of a video disc player but also in other video equipment such as a VTR, the reduction of power consumption and the most important importance in a power supply circuit having a plurality of stabilized DC power supplies. You can reinforce the constant voltage power supply,
The practical effect is great.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a power supply circuit according to an embodiment of the present invention,
FIG. 2 is a circuit diagram of a prior art example. 1 ... Power transformer, 2, 3 ... Rectifier circuit, 4, 5 ...
Stabilized power supply circuit, Q1, Q2 ... constant voltage control transistor, Q3 ... switch transistor, D1 ... constant voltage diode for voltage detection.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-55-72223 (JP, A) JP-A-58-182725 (JP, A) Practical application Sho-58-31736 (JP, U)

Claims (1)

[Claims] 1. A power supply transformer for generating a plurality of AC voltages having different voltages from a commercial power supply, a rectifier circuit for rectifying the plurality of AC voltages, and a constant voltage power supply circuit for stabilizing the output voltage thereof. A plurality of AC voltages generated by the power transformer, at least a first unstabilized voltage input to a constant voltage power supply circuit that supplies a stabilized voltage to a load with large fluctuations in power consumption; A second unstabilized voltage that is lower than the first unstabilized voltage and supplies the stabilized voltage to a load that consumes less power and has less fluctuation, and is rectified and output by each of the rectifier circuits. The second on the low voltage side
The unregulated voltage of the power transformer is set lower than the guaranteed voltage at the maximum load under the worst condition in the fluctuation of the voltage drop of the commercial power source, and the secondary winding of the power transformer is set to a voltage lower than that of the high voltage winding. The auxiliary windings are configured to be weaker than the reduced voltage of the primary windings, and the emitter terminal is connected to the stable voltage line of the constant voltage power supply circuit on the high voltage side, and the constant voltage on the low voltage side is fixed. A switching power transistor having a collector terminal connected to an unstabilized voltage of a voltage power supply circuit, a constant voltage diode having an anode connected to the base of the transistor and a cathode connected to a collector terminal of the transistor through a resistor; A switch circuit consisting of a resistor connected between the emitter terminal and the base terminal of the transistor is installed, and the unstabilized voltage on the low voltage side is the voltage drop or high voltage of the commercial power supply. Wherein the switch circuit is made conductive, the power supply circuit, characterized in that the two different voltage source and to link control when dropped from the voltage of the normal by the current consumption increased.